To produce semiconductor devices (such as transistors, capacitors, memories, light emitting devices, and solar cells) or electronic equipment (such as various displays), a photolithography method including the following steps, for example, is utilized as a method for forming a circuit on a substrate:
[1] applying a photoresist onto a substrate to form a resist coating;
[2] irradiating the resist coating with light through a photomask having a circuit pattern drawn thereon, and baking the circuit pattern;
[3] immersing the resist coating in a developing liquid to remove portions of the resist coating excluding the pattern portion;
[4] curing the resist coating remaining after the development to form a mask; and
[5] etching the substrate utilizing the resulting mask.
The resist coating formed through the above-described steps has a hydrophobic surface; therefore, for example, during the planarization of roughness on a peripheral portion (such as a bevel portion or an edge portion) of a substrate by polishing, even if polishing is performed while water is being supplied to the resist coating surface, the surface repels water and cannot be covered with water; thus, polishing debris tends to adhere to the resist coating surface, and once adhered, the polishing debris is very difficult to remove. Moreover, the adhered polishing debris can be a cause of a short in the wiring or an increase in electrical resistance, which invites a decrease in reliability.
Furthermore, because the resist coating has a hydrophobic surface, the wettability of the developing liquid during the development is poor, and unevenness in development may occur, which makes it difficult to form a desired pattern with high precision on the substrate. In addition, during washing with water and drying of the resist coating after the development, the resist pattern may collapse because of an interfacial tension between the resist coating and water. This problem has become noticeable as the resist pattern has become finer and achieved a higher aspect ratio.
As a solution to the above-described problem, a method for imparting hydrophilicity to the resist coating surface to enhance the affinity between the resist coating and water is provided. As a method for imparting hydrophilicity to the resist coating surface, Patent Literature 1 discloses a method that involves coating the resist coating surface with a surfactant or a water-soluble polymer compound. This method, however, is disadvantageous in that the coating readily peels off when water is supplied to the resist coating surface, and the effect of imparting hydrophilicity does not last.
As a method for allowing the effect of imparting hydrophilicity to last, a method for imparting hydrophilicity by dissolving a small amount of the resist coating surface with an alkaline solution is provided. Patent Literature 2 discloses a TMAH (=tetramethylammonium hydroxide) solution, for example, as the alkaline solution to be used in this method. Patent Literature 3 discloses an aqueous solution containing a quaternary ammonium hydroxide such as 2-hydroxyethyl-(N,N-dimethyl-N-lauryl)ammonium hydroxide. However, hydrophilization treatments with these alkaline solutions make the resist coating thinner, and degrade the mask characteristics, leading to a decrease in yield.